The present invention relates to a method of removal of protective group with an allyl group, which is useful for protecting hydroxyl groups or amino groups in a process for producing several kinds of organic compounds such as pharmaceuticals, agricultural chemicals, natural organic compounds or liquid crystal compounds.
When a hydroxyl group or an amino group of organic compound is protected, an allyl group is very useful skeleton as protection group under wide reaction conditions such as acidic or basic condtions. Generally, a method for changing the group protected with an allyl group into a hydroxyl group or an amino group (namely, a deprotecting method) consists of two steps, in which the allyl group is changed into an enol ether structure or enamine structure by isomerization with a transition metal such as rhodium or under basic conditions and then hydrolyzed with an acid in the presence of a mercury salt. Although the allyl group can be used as a protecting group, the utilization is limited by such an inconvenient deprotecting method.
In recent years, some deprotecting methods of one step has been reported (Akiyama et al., Tetrahedron Letters, 1991, 32, 1321-1324; Espane et al, Tetrahedron Letters, 1992, 33, 2485-2488; Nakayama et al., Chem. Pharm. Bull., 1992, 40, 1718-1720; Ito et al., J. Org. Chem., 1993, 58, 774-775; Boujerman, Tetrahedron Letters, 1994, 35, 4349-4350), and these methods are, however, impractical for technical production. The methods are limited because these are inapplicable to compounds having substituent groups or skeletons unstable under acid conditions.
The present invention aims to provide a reaction method for easily proceeding in one step under mild conditions and for changing the group protected with an allyl group into a hydroxy group or an amino group.
The present inventors have widely investigated to resolve the above problems, and have found that an allyl derivative represented by a general formula (1): 
wherein R1 shows an organic residue; A shows an oxygen atom or -NR2; and R2 shows a hydrogen atom or a organic residue, is treated with a reductant in the presence of nickel dichlorobis (diphenylphosphino) propane to obtain a compound represented by a general formula (2): 
wherein R1 shows an organic residue; A shows an oxygen atom or -NR2; and R2 shows a hydrogen atom or an organic residue, to complete the present invention.
As a starting material of the compound represented by general formula (1) for applying the method of the present invention, organic compounds having hydroxy groups or amino groups can be used without any limitation. Precursors or derivatives such as terpenes, steroids, sugars, indols, agrycone parts in macrolides, prostaglandins, and quinolones can be concretely exemplified.
These starting materials and allylhalides are treated under basic conditions to easily obtain the componds (allyl derivatives) represented by general formula (1). The other usable methods of allylation are Gyve et al., Tetrahedron Letters, 22, 3591 (1981), Satoh et al., Tetrahedron Letters, 29, 4097 (1988), Racmili et al., Tetrahedron Letters, 30, 4669 (1989), and Aniszarman et al., Carbohydr. Res., 174 (1988).
Thus obtained allyl groups are used as protection groups, desired skeletons are introduced from the starting materials via several kinds of reaction, and these groups can be changed into hydroxy groups or amino groups by the deprotecting method of the present invention.
An allyl derivative is dissolved in a solvent, nickel dichloro (diphenylphospino) propane ((dppp)NiCl2) of 1-5 mol % based on the allyl derivative is added, and the mixture is stirred. As the solvent, any solvent dissolvable the allyl derivative can be used. Diethylether, tetrahydrofuran (THF), toluene, dichloroethane, and a THF/ethanol mixed solvent can be preferably exemplified.
Diisobutylaluminum hydride, sodium borohydride, or trialkylaluminum of 1.0-1.5 equivalent (preferably 1.5 equivalent) based on the allyl derivative is added slowly to the solution in an atmosphere of argon or nitrogen at a temperature of xe2x88x9210-40xc2x0 C. (preferably 0-5xc2x0 C.). Although diisobutylaluminum hydride or trialkylaluminum may be neat, solvent such as toluene, hexane, heptane, cyclohexane, THF, or dichloromethane may be added to dissolve it. Sodium borohydride may be used as powder, or suspension with THF/ethanol mixed solvent.
The mixture is stirred at the same temperature for 5-10 minutes, and more at 10-40xc2x0 C. for 2-10 hours. The reaction solution is then diluted, water is added and the mixture is stirred for 1-2 hours. The solid material is filtered off with a filter aid such as cerite, and the solvent is distilled away. The resulting residue is subjected to common operation such as column chromatography or recrystallization to obtain a purified compound represented by general formula (2).